Phospholipase C-inhibiting peptides

ABSTRACT

The present invention relates to phopholipase C-inhibiting peptides which are represented by formula (I): ##STR1## wherein J 1  and J 2  are each hydrogen or combined together to form a single bond; W is hydrogen, a substituted or unsubstituted alkanoyl, a substituted or unsubstituted aroyl or coumaryl; X is a single bond, -Leu- or -Ser-Leu-Val-Glu-Leu-Val-Ser-Tyr-Tyr-Glu-Lys-His-Ala-Leu- (at least one of the N-terminal 14 amino acid residues may be deleted); Y is a single bond or -Pro-Val-; and Z is hydroxy or amino.

TECHNICAL FIELD

The present invention relates to novel peptides which inhibit the phopholipase C (hereinafter referred to as "PLC") activity.

BACKGROUND ART

PLC, e.g., inositolphospholipid PLC (hereinafter referred to as "PI-PLC") was separated and purified from various tissues for the purpose of elucidation of intracellular signal transduction pathway and the existence of nine isozymes in four types (α, β, γand δ) has been demonstrated. Type γ is known to occur in two kinds, γ₁ and γ₂ (S. G. Rhee et al., Science, 244, 546-550 (1989); Y. Homma et al., Biochem.J., 269, 13-18 (1990)). Both kinds have been shown to play an important role in signal transduction of growth factors. The structural feature of the β, γ and δ types is that they contain an oncogene src-associated region, SH2/SH3 region, between I and II regions common to β, γ and δ. SH2 region in the γ type is essential for the interaction with a receptor-type tyrosine kinase (D. Anderson et al., Science, 250, 979-982 (1990)). Although the function of SH3 region in the γ type has not been clear, it is presumably important for the interaction with cytoskeletons. Recently, the oncogene crk having SH2/SH3 region but not kinase region was found and this has highlighted the possibility that the regulation disorder (abnormal activity of PI-PLC) and abnormal cell proliferation as mediated by SH2/SH3 region may induce tumor. There are many other reports that review the association of increased PLC levels with pathologic conditions:

PLC is associated with the system of platelet activation by thrombin (J. Biol. Chem., 261, 16838-16847 (1986)); PLC activity is associated with histamine release (J. Cell Biol., 105, 2745-2750 (1987)); PLC is associated with the system of signal transduction by a receptor for N-formyl-methionyl-leucyl-phenylalanine which is known to induce inflammation via granulocytes and polymorphonuclear leukocytes (PMN) (Science, 232, 97-100 (1986)); the β chain of a platelet-derived growth factor (PDGF) is expressed in a large amount in arteriosclerotic lesions (Science, 248, 1009 (1990)); PLC-γ₂ is present as a component in the signal transduction system for the proliferation of PDGF-dependent vascular smooth muscle cells and hence is closely associated with the smooth muscle cell proliferation system (Biochem. Biophys. Res. Commun., 156, 846-854 (1988); Biochem.J., 290, 649-653 (1993)); and PLC is increased in Alzheimer's disease (Am. J. Pathol., 139, 737-742 (1991)). Hence, it is expected that the aforementioned diseases can be alleviated by inhibiting the PLC activity and there is a need for agents that inhibit the PLC activity.

The following peptides are disclosed in J. Biol. Chem., 267, 21844-21849 (1992) as being capable of inhibiting the PLC activity:

Ser-Leu-Val-Glu-Leu-Val-Ser-Tyr-Tyr-Glu-Lys-His-Ala-Leu-Tyr-Arg-Lys-Met-Arg-Leu-Arg-Tyr-Pro-Val,

Ser-Tyr-Tyr-Glu-Lys-His-Ala-Leu-Tyr-Arg-Lys-Met, Glu-Lys-His-Ala-Leu-Tyr-Arg-Lys-Met,

Glu-Lys-His-Ala-Leu-Tyr-Arg-Lys-Met-Arg-Leu-Arg-Tyr-Pro-Val,

Leu-Tyr-Arg-Lys-Met-Arg-Leu-Arg-Tyr-Pro-Val,

Tyr-Arg-Lys-Met-Arg-Leu-Arg-Tyr, and

Arg-Lys-Met-Arg-Leu-Arg.

DISCLOSURE OF THE INVENTION

According to the present invention, phopholipase C-inhibiting peptides which are represented by formula (I) (hereinafter referred to as "Compound(s) (I)") can be provided: ##STR2## wherein J¹ and J² are each hydrogen or combined together to form a single bond; W is hydrogen, a substituted or unsubstituted alkanoyl, a substituted or unsubstituted aroyl or coumaryl; X is a single bond, -Leu- or -Ser-Leu-Val-Glu-Leu-Val-Ser-Tyr-Tyr-Glu-Lys-His-Ala-Leu- (at least one of the N-terminal 14 amino acid residues may be deleted); Y is a single bond or -Pro-Val-; and Z is hydroxy or amino.

In the definition of Compounds (I), the substituted or unsubstituted alkanoyl may be exemplified by those having 1-20 carbon atoms such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl, caprylayl, lauroyl, myristoyl, palmitoyl, and stearoyl. Exemplary substituents include carboxy, alicyclic alkyl, and phenyl. Exemplary alicyclic alkyls include those having 3-8 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. The substituted or unsubstituted aroyl may be exemplified by benzoyl and naphthoyl. Exemplary substitutents include hydroxy groups and the number of substituents is 1-3.

The abbreviations for the amino acids and their protective groups used herein follow the recommendations by IUPAC-IUB Commission on Biochemical Nomenclature (Biochemistry, 11, 1726 (1972)).

The abbreviations for the amino acids and protective groups are as follows.

Val:L-Valine

Leu:L-Leucine

Lys:L-Lysine

Met:L-Methionine

Arg:L-Arginine

Tyr:L-Tyrosine

Cys:L-Cysteine

Pro:L-Proline

t-Boc:t-Butyloxycarbonyl

t-Bu:t-Butyl

Fmoc:9-Fluorenylmethyloxycarbonyl

Pmc:2,2,5,7,8-Pentamethylchroman-6-sulfonyl

Trt:Trityl

The abbreviations for the side-chain protected amino acids are as follows.

Fmoc-Tyr(t-Bu)-OH: N.sup.α -9-Fluorenylmethyloxycarbonyl-O-t-butyl-L-tyrosine

Fmoc-Lys(t-Boc)-OH: N.sup.α -9-Fluorenylmethyloxycarbonyl-N⁶⁸ -t-butyloxycarbonyl-L-lysine

Fmoc-Arg(Pmc)-OH: N.sup.α -9-Fluorenylmethyloxycarbonyl-N.sup.δ -2,2,5,7,8-pentamethylchroman-6-sulfonyl-L-arginine

Fmoc-Cys(Trt)-OH: N.sup.α -9-Fluorenylmethyloxycarbonyl-S-trityl-L-cysteine

The abbreviations for the reaction solvents and reaction reagents are as follows.

PyBOP: Benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate

HOBt: N-Hydroxybenzotriazole

NMM: N-Methylmorpholine

DMF: N,N-Dimethylformamide

TFA: Trifluoroacetic acid

The manufacturer of the caboxylic acid used for N-terminus modification is as follows:

n-Caprylic acid: TOKYO KASEI KOGYO CO., LTD.

Specific examples of compounds (I) are shown in Table 1.

                                      TABLE 1                                      __________________________________________________________________________            SEQ                                                                     COMPOUND                                                                              ID                                                                      NO.    NO:                                                                               SEQUENCE                                                             __________________________________________________________________________     (I-1)  1  HCysLeuTyrArgLysMetArgLeuArgTyrProValCysNH.sub.2                     (I-2)  2                                                                                  ##STR3##                                                            (I-3)  3  CH.sub.3 (CH.sub.2).sub.6 COCysLeuTyrArgLysMetArgLeuArgTyrProVal               ysNH.sub.2                                                           (I-4)  4                                                                                  ##STR4##                                                            __________________________________________________________________________

Compounds (I) can be prepared by a solid phase synthetic method using an automatic peptide synthesizer. A solid phase support to which a peptide prepared by the solid phase method has been coupled is treated with hydrogen fluoride or TFA, whereby the peptide is liberated from the solid support, and at the same time, the protective groups at amino acid side chains are removed. The amidation of C-terminal amino acids can be performed with p-Methyl-Benzhydrylamine(BHA)-Resin (Applied Biosystems, Inc., Foster City, Calif., USA; hereinafter referred to as "ABI") in the case where a peptide synthesizer available from ABI is uesd, and with Rink Amide-Resin or Rink Amide-MBHA (4-methylbenzhydrylamine)-Resin (available from Carbiochem-Novabiochem Japan) in the case where a peptide synthesizer available from Shimadzu is used. The modification (acylation) of N-terminal amino acids can be performed by removal of N-terminal amino acid protective groups, followed by condensation with a carboxylic acid component using a condensation agent such as PyBOP/HOBt/NMM in the same manner as in extension of peptide chains, or by condensation with an activated carboxylic acid such as an anhydride of a carboxylic acid and an acid chloride. The aforementioned reactions are conducted on a synthetic resin and the desired peptide derivative is obtained by cleaving it from the resin after the end of the reaction. The crude peptide product thus obtained is purified by high performance liquid chromatography (hereinafter referred to as "HPLC") using a reversed-phase column to yield a purified product.

Furthermore, cyclic peptides having an S--S bond can be obtained if linear peptides obtained in the above manner are air-oxidized in an aqueous solution of a weak base, or oxidized with an oxidizing agent such as potassium ferrocyanide or glutathione (oxidized form).

Compounds (I) provided by the present invention exhibit an excellent PLC-inhibiting activity, cell proliferation-inhibiting activity and antimicrobial activity.

The PLC-inhibiting activity, cell proliferation-inhibiting activity and antimicrobial activity of Compounds (I) are illustrated in the following Experimental Examples 1, 2 and 3, respectively.

EXPERIMENTAL EXAMPLE 1

PLC-INHIBITING ACTIVITY

A sample of PLC-γ₁ was prepared from bovine thymus according to the method described in Y. Homma et al., Biochem.J., 269, 13 (1990).

A solution having the composition shown in Table 2 was prepared on ice and the reaction was initiated by heating it to 37° C. After incubation for 10 minutes, 2 ml of a chloroform-methanol (2:1, V/V) mixed solution was added to stop the reaction. The produced inositol phosphate was extracted with 0.5 ml of 1N hydrochloric acid. The extract was separated into two liquid phases by centrifugation (2000×g, 3 minutes) and the amount of ³ H in the supernatant (0.7 ml) was measured with a scintillation counter.

                  TABLE 2                                                          ______________________________________                                         Solution                 Volume (μl)                                        ______________________________________                                         Sample (0.2 μg of Purified PI-PLC-γ.sub.1 preparation)                                         10                                                    Reaction solution        30                                                    1) 1M MES.sup.(a) NaOH buffer (pH 6.0)                                                                  2.5                                                   2) 1 mM CaCl.sub.2       5                                                     3) 20 mg/ml Bovine serum albumin                                                                        2.5                                                   4) Test peptide solution.sup.(b)                                                                        20                                                    Substrate.sup.(c)        10                                                    ______________________________________                                          .sup.(a) 2-(N-Morpholino)ethanesulfonic acid                                   .sup.(b) The test peptides and their concentrations in aqueous solution        are shown in Table 3.                                                          .sup.(c) Phosphatidylinositol 4,5bisphosphoric acid (PIP.sub.2) (500           μg), phosphatidylethanolamine (150 μg) and  .sup.3 H!PIP.sub.2 (37       kBg) were mixed in a small amount of chloroform. After drying lipids unde      a nitrogen stream, 1 ml of 0.1M KCl was added and sonication was               performed.                                                               

Percent inhibition (X) was calculated from the following equation.

    X(%)=(A-C)/(B-C)X100

where A is the obtained value of specific radioactivity, B is the value of specific radioactivity when the same amount of water was added instead of an aqueous solution of a test peptide, and C is the value of specific radioactivity when the same amount of water was added instead of a sample and an aqueous solution of a test peptide.

The thus determined percent inhibitions by the test peptides are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         Compound     Concentration (μM)                                                                       Inhibition (%)                                       ______________________________________                                         (I-2)        240          65                                                   (I-4)        220          56                                                   ______________________________________                                    

EXPERIMENTAL EXAMPLE 2

CELL PROLIFERATION-INHIBITING ACTIVITY

The cell proliferation-inhibiting activity of the test peptides was determined using a cell proliferation-detecting kit available from Amersham in the following manner.

KMS-4 cells (M. Nanba et al., International Journal of Cancer, 32, 697 (1983)) were added to a DMEM medium containing a 10% fetal calf serum (available from Nissui Pharmaceutical) and the cell concentration was adjusted to 1-2×10⁴ cells/ml. The resulting cell suspension (1 ml) was then placed in each well of a 24-well plate (available from Corning) and incubated in a CO₂ incubator (37° C., 5% CO₂) for 2 days. Subsequently, the medium was replaced with a fresh DMEM medium containing a 10% fetal calf serum, and a test peptide was added, followed by incubation for 17 hours. Then, the medium was replaced with a serum-free DMEM medium, and 0.5 ml of a solution prepared by diluting labeled 5-bromo-2'-deoxyuridine reagents (BrdU) and 5-fluoro-2'-deoxyuridine (FdU) (10:1) 1000 times with a serum-free DMEM was added to each well, followed by incubation for 2 hours. Then, the medium was removed and the cells were fixed with an acetic acid-ethanol solution. The fixed cells were stained according to the procedure for a cell proliferation-detecting kit available from Amersham and further stained with a 1% Giemsa solution (available from Merck). The number of cells which incorporated BrdU and the total number of cells were counted within one visual field (about 200 cells) under microscopic examination and the percentage (%) of the stained cell counts per visual field was calculated. The above procedure was repeated 10 more times and the mean value was taken to show the cell proliferation activity (%).

Cell proliferation-inhibiting activity was expressed by percent cell proliferation inhibition (X) which was calculated from the following equation.

    X(%)=(1-B/A)X100

where A is the proliferation activity when no peptide was added, and B is the proliferation activity when a test peptide was added.

The thus determined percent cell proliferation inhibitions by the test peptides are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         Compound     Concentration (μM)                                                                       Inhibition (%)                                       ______________________________________                                         (I-2)        5            59                                                   (I-4)        6            61                                                   ______________________________________                                    

EXPERIMENTAL EXAMPLE 3

ANTIMICROBIAL ACTIVITY

Antimicrobial activity was determined by an agar dilution method using a medium consisting of Bacto-tryptone (available from Difco) (3 g/l), meat extract (1 g/l), glucose (1 g/l) and agar (16 g/l) (pH 7.0).

When Proteus vulgaris ATCC6897 was used as a test bacterium, the minimum inhibitory concentrations (MIC) of Compounds (I-3) and (I-4) were each 166 μg/ml.

BEST MODE FOR CARRYING OUT THE INVENTION

The physicochemical properties shown in the following examples were measured with the apparatus listed below.

Mass spectrometric analysis: Nihon Denshi JMS-HXL110A

Amino acid analysis: Waters pico tag

The following Examples 1-4 will illustrate peptide synthesis using the peptide synthesizer PSSM8 available from Shimadzu with reagents and solvents available from Shimadzu according to a synthesis program developed by Shimadzu. Amino acid condensation reactions were conducted by the Fmoc method (Peptide Synthesis--Its Fundamentals and Experiments, Nobuo Izumiya, et al., (Maruzen)) under standard conditions.

Protected amino acids and reagents available from Kokusan Kagaku, Peptide Institute, Carbiochem-Novabiochem Japan were used as required.

EXAMPLE 1

Synthesis of Compound (I-1: SEQ ID NO:1)

A support resin (60 mg) combined with 4-(2,4-dimethoxyphenyl-Fmoc-aminomethyl)-phenoxy group was placed in a reactor in an automatic peptide synthesizer, treated and washed according to the synthesis program developed by Shimadzu in the following manner:

(1) Washing with DMF (3 min)

(2) Treating with a DMF solution containing 30% piperidine (4 min×2)

(3) Washing with DMF (1 min×5)

(4) Adding Fmoc-Cys(Trt)-OH (300 μmol), PyBOP (300 μmol), HOBT (300 μmol), and NMM (450 μmol) to the support resin treated in steps (1) to (3), and stirring the mixture for 30 minutes.

(5) Washing with DMF (1 min×5)

Thus, Fmoc-Cys(Trt) was coupled to the support.

Subsequently, washing and deprotection steps (1)-(3) were performed and a condensation reaction was then conducted using Fmoc-Val-OH in step (4), followed by washing step (5) to couple Fmoc-Val-Cys(Trt) to the support resin. Steps (1)-(5) were sequentially repeated using 300 μmol of Fmoc-Pro-OH, Fmoc-Tyr(t-Bu)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Leu-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Met-OH, Fmoc-Lys(t-Boc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Tyr(t-Bu)-OH, Fmoc-Leu-OH, and Fmoc-Cys(Trt)-OH in step (4) to give a protected peptide coupled to the support resin.

The obtained support resin was then washed thoroughly with methanol and butylether and dried for 2 hours under reduced pressure. One milliliter of 10% TFA/methylene chloride was charged into the reactor containing the dried support resin, followed by stirring. A solution was collected by dropping under gravity from the bottom of the reactor. The above procedure was repeated twice except that 1 ml of 20% TFA/methylene chloride was added. Removal of the solvent from the collected solutions with an evaporator gave a peptide cleaved from the resin. Furthermore, the peptide was deprotected by adding 1 ml of a mixed solution consisting of 82.5% TFA, 5% H₂ O, 5% thioanisole, 2.5% ethanedithiol, 3% ethylmethylsulfide, and 2% thiophenol and leaving the mixture to stand for 8 hours at room temperature. About 2 ml of ether was added to the resulting solution to precipitate a crude peptide. The collected crude peptide (52.6 mg) was purified by HPLC using a reversed-phase column (NUCLEOSIL 5C18, 20×250 mm). A fraction containing the desired compound was obtained by elution with a linear concentration gradient of acetonitrile in water containing 0.1% TFA and detection at a wavelength of 220 nm. The fraction was lyophilized to yield Compound (I-1) (16.5 mg).

Mass spectrometric analysis: M+H=1699

Amino acid analysis: Arg 3.1 (3), Pro 1.0 (1), Tyr 2.0 (2), Val 0.9 (1), Met 1.0 (1), Leu 2.0 (2), Lys 1.1 (1), Cys 1.8 (2)

EXAMPLE 2

Synthesis of Compound (I-2: SEQ ID NO:2)

Compound (I-1) (15.6 mg) was dissolved in 15.6 ml of water. To the resulting solution were added 1.56 ml of 200 mM phosphate buffer (pH 7.0) and 0.32 ml of 10 mM glutathione (oxidized form) and cyclization reaction was conducted at 4° C. for 19 hours. The cyclized product was purified by HPLC to yield Compound (I-2) (3.6 mg).

Mass spectrometric analysis: M+H=1697

Amino acid analysis: Arg 3.1 (3), Pro 1.0 (1), Tyr 2.0 (2), Val 0.9 (1), Met 1.0 (1), Leu 2.0 (2), Lys 1.1 (1), Cys 1.8 (2)

EXAMPLE 3

Synthesis of Compound (I-3: SEQ ID NO:3)

Condensation reaction was performed as in Example 1 using 60 mg of the support resin and the following N-protected amino acids: Fmoc-Cys(Trt)-OH, Fmoc-Val-OH, Fmoc-Pro-OH, Fmoc-Tyr(t-Bu)-OH, Fmoc-Arg (Pmc)-OH, Fmoc-Leu-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Met-OH, Fmoc-Lys(t-Boc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Tyr(t-Bu)-OH, Fmoc-Leu-OH, and Fmoc-Cys(Trt)-OH and n-caprylic acid. As in Example 1, a peptide was cleaved from the resin and deprotected to yield a crude product (62.4 mg). A portion (25.4 mg) of the crude product was purified by HPLC to yield Compound (I-3) (21.5 mg).

Mass spectrometric analysis: M+H=1825

Amino acid analysis: Arg 3.0 (3), Pro 1.0 (1), Tyr 2.0 (2), Val 0.9 (1), Met 1.0 (1), Leu 2.0 (2), Lys 1.0 (1), Cys 2.0 (2).

EXAMPLE 4

Synthesis of Compound (I-4: SEQ ID NO:4)

Compound (I-3) (9.0 mg) was dissolved in 9 ml of water. To the resulting solution were added 1 ml of 200 mM phosphate buffer (pH 7.0), 0.4 ml of 10 mM glutathione (oxidized form) and 18 ml of 9M urea and cyclization reaction was conducted at 4° C. for 45 hours. The cyclized product was purified by HPLC to yield Compound (I-4) (4.1 mg).

Mass spectrometric analysis: M+H=1823

Amino acid analysis: Arg 3.0 (3), Pro 1.0 (1), Tyr 2.0 (2), Val 0.9 (1), Met 1.0 (1), Lys 1.0 (1), Cys 2.0 (2)

INDUSTRIAL APPLICABILITY

According to the present invention, peptides having the phospholipase C-inhibiting activity can be provided.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 4                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 13                                                                 (B) TYPE: AMINO ACID                                                           (D) TOPOLOGY: LINEAR                                                           (ii) MOLECULE TYPE: PEPTIDE                                                    (ix) FEATURE:                                                                  (A) NAME/KEY: MODIFIED-SITE                                                    (B) LOCATION: 13                                                               (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 13                                      IS L- CYSTEINAMIDE                                                             (xi) SEQUENCE DESCRIPTION:SEQ ID NO:1:                                         CysLeuTyrArgLysMetArgLeuArgTyrProValXaa                                        1510                                                                           (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 13                                                                 (B) TYPE: AMINO ACID                                                           (D) TOPOLOGY: LINEAR                                                           (ii) MOLECULE TYPE: PEPTIDE                                                    (ix) FEATURE:                                                                  (A) NAME/KEY: DISULFIDE-BONDS                                                  (B) LOCATION: 1..13                                                            (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 13                                      IS L- CYSTEINAMIDE                                                             (xi) SEQUENCE DESCRIPTION:SEQ ID NO:2:                                         CysLeuTyrArgLysMetArgLeuArgTyrProValXaa                                        1510                                                                           (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 13                                                                 (B) TYPE: AMINO ACID                                                           (D) TOPOLOGY: LINEAR                                                           (ii) MOLECULE TYPE: PEPTIDE                                                    (ix) FEATURE:                                                                  (A) NAME/KEY: MODIFIED-SITE                                                    (B) LOCATION: 1                                                                (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 1 IS                                    N-(N- CAPRYLOYL) - L-CYSTEINE                                                  (ix) FEATURE:                                                                  (A) NAME/KEY: MODIFIED-SITE                                                    (B) LOCATION: 13                                                               (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 13                                      IS L- CYSTEINAMIDE                                                             (xi) SEQUENCE DESCRIPTION:SEQ ID NO:3:                                         XaaLeuTyrArgLysMetArgLeuArgTyrProValXaa                                        1510                                                                           (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 13                                                                 (B) TYPE: AMINO ACID                                                           (D) TOPOLOGY: LINEAR                                                           (ii) MOLECULE TYPE: Peptide                                                    (ix) FEATURE:                                                                  (A) NAME/KEY: DISULFIDE-BONDS                                                  (B) LOCATION: 1..13                                                            (C) IDENTIFICATION METHOD: EXPERIMENT                                          (ix) FEATURE:                                                                  (A) NAME/KEY: MODIFIED-SITE                                                    (B) LOCATION: 1                                                                (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 1                                       IS N -(N- CAPRYLOYL)-L-CYSTEINE                                                (ix) FEATURE:                                                                  (A) NAME/KEY: MODIFIED-SITE                                                    (B) LOCATION: 13                                                               (C) IDENTIFICATION METHOD: EXPERIMENT                                          (D) OTHER INFORMATION: XAA AT LOCATION 13                                      IS L- CYSTEINAMIDE                                                             (xi) SEQUENCE DESCRIPTION:SEQ ID NO:4:                                         XaaLeuTyrArgLysMetArgLeuArgTyrProValXaa                                        1510                                                                           __________________________________________________________________________ 

We claim:
 1. A phospholipase C-inhibiting peptide which is represented by formula (I): ##STR5## wherein J¹ and J² are each hydrogen or combined together to form a single bond; W is hydrogen, an alkanoyl having from 1 to 20 carbon atoms, an aroyl or coumaryl; X is a single bond, -Leu- or -Ser-Leu-Val-Glu-Leu-Val-Ser-Tyr-Tyr-Glu-Lys-His-Ala-Leu- wherein at least one of the N-terminal 14 amino acid residues may be deleted; Y is a single bond or -Pro-Val-; and Z is hydroxy or amino, with the proviso that when J¹ and J² are each hydrogen W is an alkanoyl having from 1 to 20 carbon atoms, an aroyl or coumaryl.
 2. The peptide of claim 1, wherein X is -Leu- and Y is -Pro-Val-.
 3. The peptide of claim 2, wherein Z is amino.
 4. The peptide of claim (1), (2) or (3), wherein said peptide is selected from the group consisting of peptides having amino acid sequences shown by SEQ. ID Nos. 2 (compound I-2), 3 (compound I-3) and 4 (compound I-4).
 5. The peptide according to claim 1 wherein the alkanoyl is selected from the group consisting of formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl, caprylyl, lauroyl, myristoyl, palmitoyl, and stearoyl.
 6. The peptide according to claim 1 wherein the alkanoyl is substituted with an alicyclic alkyl having 3 to 8 carbon atoms.
 7. The peptide according to claim 6 wherein the alicyclic alkyl is selected from the group consisting of cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
 8. The peptide according to claim 1 wherein the aroyl is selected from the group consisting of benzoyl and naphthoyl.
 9. The peptide according to claim 1 wherein the aroyl is substituted with 1 to 3 hydroxy groups. 